Pulse widening circuit



y 25, 1954 c. R. HOLLAND 2,679,586

- PULSE WIDENING CIRCUIT Filed Sept. 27, 1950 ouTPUT SOURCE OF INPUT SIGNAL Pi 2c.

TME

In ven tor:

Charles R- H \and,

y M, Z) His Attorney,

. multivibrator to the unstable condition.

Patented May 25, 1954 PULSE WIDENIN G CIRCUIT Charles R. Holland, Syracuse, N. 'Y., .assignor to General Electric Company, a corporation of New York Application September 27, 1950, Serial No. 187,119

3 Claims.

My invention relates to circuits for widenin a pulse voltage.

An ject of my invention is to provide a new and improved circuit for producing in response to a pulse of voltage of '3 redetermined duration a second pulse of longer duration.

Another object of my invention is to provide a new and improved circuit for increasing the duration of a pulse .of voltage by a determinable amount.

In the attainment of the foregoing objects, I provide a one-shot multivibrator circuit utilizing a pair of electron discharge devices having a common cathode resistor. In the absence of a signal to the multivibrator, i. e. the control electrodes are at substantially the same voltage as the cathodes, one of the devices is conductive and the other device is .nonconductive. Hereinafter, this is referred to as the normal condition.

A negative pulse of voltage sup lied to the control electrode or the normally conductive device causes it to be nonconductive and the other device to be conductive. Hereinafter this is referred to as the unstable condition. Following the pulse, the multivibrator remains in this .unstable condition until a coupling capacitor in the multivibrator has discharged.

In this circuit, an input voltage pulse is supplied to a cathode follower .stage .and coupled from the output thereof to the multivibrator through a unilateral impedance to the control electrode of the normally conductive device. The unilateral impedance is arranged such that on y negative signals pass therethrough to trip the The multivibrator then remains in the unstable condition for the duration of the input pulse and until the heretofore-mentioned coupling capacitor has discharged. Because the coupling capacitor is maintained in the charged condition by the input pulse, discharge therefrom does not begin until the end of the pulse. The unilateral impedance, of course, prevents it from discharging back through the cathode follower circuit. In consequence thereof, a pulse of voltage is produced by the multivibrator which has a time width equal to the sum .of the time width of the input pulse and of the time required for the coupling capacitor to discharge.

For further objects and advantages and for a better understanding of my invention, .attention is now directed to the following description and accompanying drawing and also to the appended claims. In the drawing, Fig. l is a schematic circuit diagram illustrating an embodiment of my invention; and Figs. 2a, 2b, and 2c are wave shapes which are applicable, for illustrative purposes, to the circuit of "Fig. l.

Referring to Fig. 1, an electron discharge device I is provided with an anode 2, a control electrode 3, and-a cathode 4. Device I is connectedas a cathode follower with cathode 4 coupled to ground through a series connection .of a pair of cathode resistors 5 and 6. A signal supplied from source I is coupled through a couplin network comprising a capacitor 8 and a resistor 9 to control electrode 3. An output signal from cathode follower I, which appears across resistors 5 and 6 and is of the same polarity as the signal applied to terminal "I, is coupled through a unilateral impedance device ID to the control electrode of an electron discharge device II. Davice I0 is shown in the drawing as a diode discharge device, but may be any one of many conventional unilateral impedances. Electron discharge device II and another electron discharge device I2 are connected in a one-shot multivibrator circuit. The cathode of devices I I and 1-2 are directly connected together and are coupled to ground through a common cathode resistor I3 and the parallel circuit arrangement of a resistor I4 and a capacitor I5. The control electrode of device I2 is directly connected to the junction of resistor I3, resistor I4, and capacitor I5. A coupling capacitor I6 is connected between the .control electrode of device I I and the anode of device I2. Devices H and I2 are provided with anode load resistors 11 and I8 respectively. A resistor I9 is interconnected between the control electrode of device II and the cathodes of devices II and I2 to provide a discharge path for capacitor I6. In the particular embodiment shown, the output of the multivibrator circuit appears at the anode of device II.

In the absence of a signal from source I, device I is conductive, device IIi in noncondu-ctive, device II is conductive, and device I2 is nonconductive. Device I2 is maintained nonconductive by the bias supplied from the voltage drop across resistor I3. For a better understanding of this circuit, it is assumed that an input voltage wave of the type shown in Fig. 2a is supplied from source I and that this wave has an amplitude great enough to cut on device I. A similar wave then appears across resistors 5 and .i3 .and is coupled through device It to the control electrode of device I "I. -Device II] is connected so as to conduct electrons from cathode 4 to the control electrode of device II and is maintained nonconductive in the absence of input signal by the positive voltage on its cathode produced across resistors 5 and 6. Resistors I3, I4, and I9 are selected such that the anode of device I0 is at a voltage "which is less than the cathode voltage thereof. Therefore, only negative pulses are cou- Died from the cathode follower to the multivibrator and device III performs the added function of preventing false tripping while preventing capacitor it from discharging theretnrough. The negative pulse across resistors 5 and '6 i's'coupled by device 'I 0 to the control electrode of device II, cutting it off. The multivibrator is thus tripped to the unstable condition in which device I2 is conductive. Immediately following the input pulse, the multivibrator does not revert to the stable condition because device H is held nonconductive by the voltage drop across resistor 19 a as capacitor l6 discharges therethrough.

Fig. 2b illustrates the shape of the voltage wave appearing on the control electrode of device II. It should be noted that the exponential rise in this voltage following'the end of the input pulse is due to the voltage drop across resistor 19 which decreases as the voltageacross capacitor [6 decreases. As is well known in the art, the voltage across a discharging capacitor decreases exponentially.

Fig. 20 illustrates the output voltage wave of the multivibrator appearing at the anode of device ll. This wave continues at a. high level until the voltage across resistor l9 decreases to a level which permits conduction of device I I. At this time, device ll becomes conductive and the voltage on the anode thereof immediately returns to normal. This produces the sharp trailing edge of the wave.

The following circuit values are not meant to limit the invention thereto, but they are included because they have been found to effect efficient operation of the particular embodiment of this invention described herein.

Resistor 430 ohms. Resistor 8 7500 ohms. Resistor9 1 megohm. Resistor l3 680 ohms. Resistor l4 3300 ohms. Resistor ll 5100 ohms. Resistor l8 5100 ohms. Resistor l9 33,000 ohms. Capacitor 8 0.1 mfd. Capacitor l5 20 mfd. Capacitor l6 30 mfd. Devicel Az-IZATW. Device H1 /z-12AT'Z. Device H 1/2-12AT7. Device l2 /g-12AT7. B+ 2'75 volts D.C.

Modifications of this invention will occur to those skilled in the art and it is desired to be understood, therefore, that this invention is not to be limited to the particular embodiment disclosed, but that the appended claims are meant to cover all the modifications which are within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A circuit for increasing the time duration of a voltage pulse comprising first and second electron discharge devices, each of said devices being provided with an anode, a cathode and a controlselectrode, said devices being provided with a common cathode resistor, an electrical connection for supplying a bias to said second discharge device from said cathode resistor, a resistor connected between the control electrode and the cathode of said first discharge device, a coupling capacitor interconnected between the anode of said second discharge device and the control electrode of said first discharge device, a resistor and a capacitor connected in parallel relation and located in the common cathode circuit of said first and second discharge devices, a cathode follower including a third electron discharge device being provided with an anode, a cathode and a control electrode, and a cathode resistor, a unilateral impedance connected to con- '4 duct electrons from the cathode of said third discharge device to thecontrol electrode of said first discharge device to produce a voltage pulse at the anode of said first device which is wider than a voltage pulse supplied to the control electrode of said third discharge device.

2. The combination, in a system for converting pulses of short duration to pulses of longer duration, of a pair of electron discharge devices each having an anode, a cathode and a grid, a source of operating potential connected between the anode of each of said devices and the cathode thereof, circuit means to render either device conductive when the other is nonconductive, means to apply said pulses of short duration to the grid of one of said devices that is conductive to render it nonconductive whereby the other device becomes conductive, said means including a unilaterally conducting device having an anode and a cathode and a resistance connected in that order in series between the grid and cathode of said one device with the anode connected to the grid, said short pulses being applied in a polarity across said resistance to cause conduction of said runilaterally conducting device to cause a lowering of the potential of said grid during the occurrence of said short pulses, a resistance connected between said source of operating potential and the anode of said other device, and a condenser connected between the said anode of said other device and the grid of said one device whereby upon termination of said short pulses said first device is maintained nonconductive for a predetermined interval by the charge on said condenser whereby the current pulses in said other device have a duration of said shorter pulse plus said predetermined interval.

3. The combination, in a system for converting pulses of short duration to pulses of longer duration, of a pair of electron discharge devices each having an anode, a cathode, and a grid, a source of operating potential connected between the anode of each of said devices and the cathode thereof, circuit means to render either device conductive when the other is nonconductive, means to apply said pulses of short duration to the grid of one of said devices that is conductive to render it nonconductive whereby the other device becomes conductive, and means including a unilaterally conducting device having an anode and a cathode connected between the grid and cathode of said one device with the anode connected to the grid, said short pulses being applied in a polarity across said resistance to cause conduction of said unilaterally conducting device to cause a lowering of the potential of said grid during the occurrence of said short pulses, a resistance connected between said source of operating potential and the anode of said other device, and a condenser connected between the anode of said other device and the grid of said one device whereby upon termination of said short pulses said first device is maintained nonconductive for a predetermined interval by the charge on said condenser whereby the current pulses in said other device have a duration of said shorter pulse plus said predetermined interval.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,405,237 Ruhlig Aug. 6, 1946 2,416,158 Coykendall Feb. 18, 1947 2,419,340 Easton Apr. 22, 1947 2,526,551 Gano Oct. 1'7, 1950 

